Ram ProMaster City HVAC Mystery: No Blower Speed 1 & AC Issues Solved

Diagnosing the HVAC Enigma

• 💡 The Ram ProMaster City presented with a peculiar HVAC issue: no blower on speed 1, yet all other speeds (2, 3, 4) functioned.
• ⚠️ A strange symptom was observed: the A/C light would turn off on speeds 2, 3, and 4, only to turn on when set to speed 1 (where the blower failed).
• 🔍 Initial assumption of a simple A/C leak was quickly dismissed due to the unique blower and A/C light behavior.

Scan Tool Insights and Initial Tests

• 💻 A scan tool was employed to check for relevant HVAC codes or inhibit reasons, but none were immediately apparent.
• 📊 Data stream analysis revealed that the HVAC controller seemed to misinterpret the fan speed knob position, registering speeds 2, 3, and 4 as zero.
• ⚡ Despite the confusing readings, the A/C system itself was functional, as demonstrated by the compressor engaging and providing cold air when the system was manually activated via the scan tool.

The Blower Resistor Hypothesis

• ⚙️ The primary suspect became the blower motor resistor, as it directly controls fan speeds and is a common failure point for low-speed issues.
• ⚠️ The video highlights the difficulty in accessing and removing the blower resistor, requiring specialized tools and techniques due to its design.
• 🛠️ After a challenging removal process, the old resistor was replaced with a new Mopar part.

Resolution and Lingering Questions

• ✅ Upon installation of the new blower resistor, all fan speeds (1-4) were restored, and crucially, the A/C system now functions correctly across all speeds.
• 🤔 The exact electronic interaction between the blower resistor and the HVAC controller remains a mystery, as the scan tool data still showed unusual readings for the knob position, yet the problem was resolved.
• 💡 The takeaway is that a faulty blower resistor, even without setting obvious codes, can cause complex HVAC system malfunctions, including A/C operation issues.